docs: Capitalize Markdown consistently.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

docs/documentation/api.md

@@ -30,7 +30,7 @@ Our API documentation is defined by a few sets of files:
   [OpenAPI configuration](../documentation/openapi.md) at
   `zerver/openapi/zulip.yaml`.
 * The top-level templates live under `templates/zerver/api/*`, and are
-  written using the markdown framework that powers our [user
+  written using the Markdown framework that powers our [user
   docs](../documentation/user.md), with some special extensions for
   rendering nice code blocks and example responses.  We expect to
   eventually remove most of these files where it is possible to
@@ -268,16 +268,16 @@ above.
    comments. The lines inside these comments are what will be displayed as the
    code example on our `/api` page.
 
-1. Finally, write the markdown file for your API endpoint under
+1. Finally, write the Markdown file for your API endpoint under
    `templates/zerver/api/`.  This is usually pretty easy to template
    off existing endpoints; but refer to the system explanations above
    for details.
 
-1. Add the markdown file to the index in `templates/zerver/help/include/rest-endpoints.md`.
+1. Add the Markdown file to the index in `templates/zerver/help/include/rest-endpoints.md`.
 
 1. Test your endpoint, pretending to be a new user in a hurry, by
    visiting it via the links on `http://localhost:9991/api` (the API
-   docs are rendered from the markdown source files on page load, so
+   docs are rendered from the Markdown source files on page load, so
    just reload to see an updated version as you edit).  You should
    make sure that copy-pasting the code in your examples works, and
    post an example of the output in the pull request.
@@ -287,7 +287,7 @@ above.
 ## Why a custom system?
 
 Given that our documentation is written in large part using the
-OpenAPI format, why maintain a custom markdown system for displaying
+OpenAPI format, why maintain a custom Markdown system for displaying
 it?  There's several major benefits to this system:
 
 * It is extremely common for API documentation to become out of date

docs/documentation/user.md

@@ -39,7 +39,7 @@ form `/help/foo`; with special cases for `/help/` going to `index.md` and
 are usually linked from `static/images/help/`.
 
 This means that you can contribute to the Zulip user documentation by just
-adding to or editing the collection of markdown files under
+adding to or editing the collection of Markdown files under
 `templates/zerver/help`.  If you have the Zulip development environment
 setup, you simply need to reload your browser on
 `http://localhost:9991/help/foo` to see the latest version of `foo.md`
@@ -100,7 +100,7 @@ your documentation to help improve its readability:
 
 * Since raw HTML is supported in Markdown, you can include arbitrary
 HTML/CSS in your documentation as needed.
-* Code blocks allow you to highlight syntax, similar to Zulip's own markdown.
+* Code blocks allow you to highlight syntax, similar to Zulip's own Markdown.
 * Anchor tags can be used to link to headers in other documents.
 * [Images](#images) of Zulip UI can be added to documentation.
 * Inline [icons](#icons) used to refer to features in the Zulip UI.
@@ -108,7 +108,7 @@ HTML/CSS in your documentation as needed.
 documentation.
 * You can create special highlight warning blocks using
 [tips and warnings](#tips-and-warnings).
-* You can create tabs using [markdown tab switcher](#tab-switcher).
+* You can create tabs using [Markdown tab switcher](#tab-switcher).
 
 ### Images
 
@@ -232,7 +232,7 @@ should be formatted as a continuation of a numbered step.
 
 ###  Tab Switcher
 
-Our markdown processor supports easily creating a tab switcher widget
+Our Markdown processor supports easily creating a tab switcher widget
 design to easily show the instructions for different
 [platforms](https://zulip.com/help/logging-out) in user docs,
 languages in API docs, etc.  To create a tab switcher, write: